1. Field of the Invention
The present invention relates to nonwoven fabric.
2. Related Art
Conventionally, nonwoven fabrics are used in a variety of fields, for example, sanitary products such as disposable diaper and sanitary napkin, cleaning products such as wipers and medical products such as masks. Such nonwoven fabrics are used in many different fields, but when actually used in products of each of those fields, it is necessary that the nonwoven fabric are manufactured with the properties and structures appropriate for their intended use.
Nonwoven fabric is manufactured by, for example, using a dry method or a wet method to form a fiber layer (fiber web) and then to bond fibers forming the fiber layer by a chemical bond method or a thermal bond method for example. Methods for bonding the fibers forming the fiber layer includes a method for applying a physical force where a plurality of needles are repeatedly inserted into the fiber layer and a method of applying a physical force where aqueous steam is jetted to the fiber layer.
However, these methods have only entangled the fibers to one another and do not adjust the orientation or arrangement of the fibers in the fiber layer, the shape of the fiber layer or the like. In other words, these methods only manufactured a simple sheet-like nonwoven fabric.
Nonwoven fabric that include openings has previously been suggested and a method has been disclosed in Japanese Unexamined Patent Publication No. Hei 6-330443 (hereinafter referred to as Patent Document 1) according to which, an opening is provided in a nonwoven fabric by sandwiching the nonwoven fabric between a stamp including a projection, such as a outwardly-protruding needle, and a supporting body receiving the projection so that the projection penetrates the nonwoven fabric to provide a three-dimensional opening for example.
When a nonwoven fabric including openings is used as a surface sheet of an absorbent article for highly viscous liquid for example, it is preferable to use a structure in which a joining section between a first open area and a second open area is reduced in size in order to increase both the diameter and ratio of the open area. However, in the case of the nonwoven fabric disclosed in Patent Document 1, a fiber assembly constituting the nonwoven fabric is pressed between the projection part and the receiving supporting body to cause concavities and convexities and openings. Thus, the joining section between the open areas has substantially the same density as that of the periphery of the open areas and the fiber orientation is mainly unchanged in the longitudinal direction. When the nonwoven fabric is used as a surface sheet in an absorbent article and the nonwoven fabric includes an arrangement of open areas among which small joining portions are provided, friction to the article in the width direction may cause fibers in the joining portion to easily unravel and result in damage to the article.